1. Field of the Invention
The invention relates to bearings and is particularly although not exclusively, applicable to bearings for railway vehicles.
2. Description of the Prior Art
U.S. Pat. No. 1,677,171 discloses an axle bearing for railway equipment comprising a journal bearing casting, a lubricant reservoir attached to one end of the bearing casting, a bushing rotatably mounted in the bearing, an axle rotatably mounted in said bushing. The axle has an end portion positioned within the reservoir and a central hole is drilled into the axle from said end portion the hole extending the full length of the journal. A plurality of radial holes extend from the central hole so that lubricant may flow from the reservoir to the centre of the bushing. A plurality of holes are drilled in the wall of the bushing to lubricate the inner surface of the liner.
The problem which this arrangements present arises from the requirement that the oil film between the top portion of the axle and the journal should be capable of withstanding the downward load of the railway vehicle supported by the bearing. To generate sufficient pressure in the oil for this purpose the axle should be slightly smaller in diameter than the inner surface of the journal so that the downward load causes the axle to run slightly off centre with respect to the bearing. Thus the annular space between the bearing and axle tapers towards the top of the axle and the film of lubricant drawn round with the shaft as it rotates in the liner is drawn into the tapering annular space and is compressed to a pressure which supports the axle surface away from the journal surface. In the bearing of U.S. Pat. No. 1,677,171 there are radial holes in the axle which will relieve any such pressure build up in the oil at the top of the axle and so the essential rise in pressure in the lubricant towards the top of the axle will not occur and there is a consequent risk of metal to metal contact between the bearing liner and axle when subjected to load.
The object of the applicant's invention is to overcome the above problem, that is to deliver the lubricant from an end reservoir of a bearing housing to a liner in the housing without preventing the build up of pressure between the axle and the liner required to support the axle and liner apart when subjected to load.